The present invention relates to a method of making semiconductor devices, in particular, devices that include copper damascene interconnects.
When making advanced semiconductor devices, copper interconnects may offer a number of advantages over those made from aluminum. For that reason, copper has become the material of choice for making such devices"" interconnects. As device dimensions shrink so does conductor widthxe2x80x94leading to higher resistance and current density. Increasing current density can increase the rate at which copper atoms are displaced when current passes through a copper conductor. Such electromigration can cause vacancies, which may lead to voids, e.g., at the interface between the copper conductor and a barrier layer that may be formed on the conductor. If a void grows to a size that creates metal separation, e.g., near a via that contacts the conductor, it may cause an open-circuit failure.
One way to prevent electromigration from causing interconnect failure is to limit the amount of current that passes through the conductor. That solution to the electromigration problem is impractical, however, because devices will operate at progressively higher currents, even as they continue to shrink. As an alternative, reliability can be enhanced by doping the interconnectxe2x80x94as adding dopants to the conductor can reduce the rate at which copper diffuses. Doping the interconnect, however, can raise its resistance significantly. To reduce RC delay that is associated with high resistance, it may be necessary to limit dopant concentrationxe2x80x94or dispense with doping altogether, e.g., when forming high speed conductors. When low level doping is required to limit conductor resistance, the electromigration mitigating impact that such doping provides is reduced.
Accordingly, there is a need for an improved process for making a semiconductor device that includes copper interconnects. There is a need for such a process that reduces electromigration without significantly raising conductor resistance. The method of the present invention provides such a process.